Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A polyhedron having 20 faces.

from The Century Dictionary.

  • noun A solid bounded by twenty planes.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Geom.) A solid bounded by twenty sides or faces.
  • noun one of the five regular polyhedrons, bounded by twenty equilateral triangules. Five triangles meet to form each solid angle of the polyhedron.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun geometry A polyhedron with twenty faces.
  • noun geometry, specifically A regular icosahedron: one of the Platonic solids, all of whose faces are regular triangles

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun any polyhedron having twenty plane faces

Etymologies

from The American Heritage® Dictionary of the English Language, 4th Edition

[Greek eikosaedron, from neuter of Greek eikosaedros, twenty-sided : eikosi, twenty; see wīkm̥tī- in Indo-European roots + -edros, -sided; see –hedron.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Ancient Greek εἰκοσάεδρον, from εἴκοσι ("twenty") + ἕδρα (hedra, "face of a geometrical solid").

Examples

  • The icosahedron is another of the five regular, or Platonic, bodies having all their sides, angles, and planes similar and equal.

    Amusements in Mathematics

  • Then, about 10 years ago, the mathematician Reidun Twarock developed a more general theory of the geometry of viruses based on the symmetries of the icosahedron, but using shapes in six dimensions, not three.

    New Angles on Biology

  • I've rolled the icosahedron and painted a few miniatures myself so it only raises my charisma to be accepted by that culture.

    Archive 2009-08-01

  • I've rolled the icosahedron and painted a few miniatures myself so it only raises my charisma to be accepted by that culture.

    The Lovecraft News Network

  • The company receives more than 1 million applications a year and identifies the top candidates through a rigorous screening process that analyzes SAT scores, grade-point averages and their performance on tests with such questions as: "How many different ways can you color an icosahedron with one of three colors on each face?"

    Google Hiring More Than 6,200 Workers This Year

  • The company receives more than 1 million applications a year and identifies the top candidates through a rigorous screening process that analyzes SAT scores, grade-point averages and their performance on tests with such questions as: "How many different ways can you color an icosahedron with one of three colors on each face?"

    Google Hiring More Than 6,200 Workers This Year

  • Then, about 10 years ago, the mathematician Reidun Twarock developed a more general theory of the geometry of viruses based on the symmetries of the icosahedron, but using shapes in six dimensions, not three.

    New Angles on Biology

  • The company receives more than 1 million applications a year and identifies the top candidates through a rigorous screening process that analyzes SAT scores, grade-point averages and their performance on tests with such questions as: "How many different ways can you color an icosahedron with one of three colors on each face?"

    Google Hiring More Than 6,200 Workers This Year

  • Join five equilateral triangles together and you have the first part of an icosahedron C.

    HERE’S LOOKING AT EUCLID

  • Only five shapes fit the bill: the tetrahedron, the cube, the octahedron, the icosahedron and the dodecahedron, the quintet known as the Platonic solids since Plato wrote about them in the Timaeus.

    HERE’S LOOKING AT EUCLID

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